Bypass Powershell to run zsh command

Question

In Powershell(pwsh) Is it possible to "bypass" Powershell to not do anything and let the underlying shell do the work?

Sometime I need to call a command, that I copy from a site or other, that includes "\" and not "´" for line break - or other parameters, that Powershell try to interpolate.

Like:

 <Powershell Function> kubectl get rolebindings,clusterrolebindings \                                      
  --all-namespaces  \
  -o custom-columns='KIND:kind,NAMESPACE:metadata.namespace,NAME:metadata.name,SERVICE_ACCOUNTS:subjects[?(@.kind=="ServiceAccount")].name' | grep name

mklement0 · Accepted Answer · 2022-02-21T19:02:25.277

and let the underlying shell do the work?

PowerShell is a shell, so there is no underlying shell as such (in the sense that PowerShell needn't be launched from another shell). However, there are platform-specific default shells: cmd.exe on Windows, and /bin/sh on Unix-like platforms.

I need to call a command, that I copy from a site or other

Before PowerShell went cross-platform, --%, the stop-parsing token was introduced in Windows PowerShell v3, precisely to address your scenario.

Given that Windows was the only supported platform at the time, the behavior is focused on cmd.exe - and even there it doesn't support cmd.exe's line continuation via line-ending ^ chars.

More generally, while it tries to emulate cmd.exe's behavior (e.g., by expanding %-enclosed tokens such as %USERNAME% as environment-variable references) without actually delegating to the latter, it doesn't do so fully.

In PowerShell Core (v6+) --% is even supported on Unix-like platforms, but is of little utility there, given that cmd.exe semantics are applied even there; notably, '...'-quoting is not supported.

(Note that PowerShell emulates one /bin/sh feature on Unix-like platforms, but only without use of
--%: globbing, i.e. the expansion of unquoted tokens such as *.txt to matching file paths).

However, you can call the platform-native shell explicitly, e.g, by passing the copied command string to sh -c on Unix-like platforms, using a (verbatim) here-string for the command string:

# Call the platform-native shell with a command crafted for it:
sh -c @'
  echo This line\
    keeps going\
    with --all-namespaces and\
    with -o custom-columns='KIND:kind,NAMESPACE'
'@

Unfortunately, there's a catch:

Up to at least v7.2.x, PowerShell's handling of embedded " chars. in arguments passed to external programs (such as sh) is fundamentally broken, requiring embedded " to be manually \-escaped:

# !! BROKEN
sh -c @'
  echo "high noon"
'@

To make this work, you have to \-escape manually:

# WORKAROUND
sh -c (@'
  echo "high noon"
'@ -replace '"', '\"')

See this answer and this GitHub issue for background information. In short: Backward-compatibility concerns prevent fixing the default behavior, but discussions are underway to at least allow opting into sane default behavior.

score 1 · Answer 2 · answered Jan 16 '20 at 22:17

Not that I'm aware of. I also don't know of any shell where this is possible, either, save for Ruby where you have the string literal operators making escapes much easier.

I would suggest that before sending strings to external commands, that you convert the PowerShell escape sequences to the target runtime escape sequences. This isn't a problem unique to PowerShell, but is easier to work with in other shells because there is more of an overlap of the special characters between other runtimes.

Bypass Powershell to run zsh command

2 Answers2